Procedure for evaporating waste lye from pulp



D. v.IAPS

April 20, 1965 PROCEDURE FOR EVAPORATING WASTE LYE FROM PULP Filed oct.19.1960

2 Sheets-Sheet 1 mln TMQSWQ 200 ul' INVENTOR.

DA N/EL J/-s lll' M23 QMM ATTRNEX April 20, 1965 D- JAFS 3,179,159

PROCEDURE FOR EVAPORATING WASTE LYE FROM PULP Filed Oct. 19. 1960 2Sheets-Sheet 2 C'O/VDNS 19 TE DA A//EL J F5 INVENTOR.

3,179,159 PRGCEDURE FOR EVAPORATING WASTE LYE FROM PULP Daniel Jfs,Warkaus, Finland, assignor to A. Ahlstrom Osakeyhtio, Warliaus Brnk,Warkaus, Finland, a corporation of Finland Filed Uct. 19, 1960, Ser. No.63,601 3 Claims. (Cl. 159-47) Evaporators employing indirect heatexchange are used especially for evaporating waste lye from the pulpindustry. For the sake of simplicity, the following descrip- `tion isconned to `apparatus designed for this purpose. In the evaporationmethod envisaged by this invention, at least part of-the lye isconducted in the opposite di- United States Patent rection from thevapour, and it is desirable for the lye .to be warmed up before it istaken on to the following stage in inverse order. For this purpose,indirect heating is provided by one or more heat exchangers, usingsecondary vapour or condensate as the heating medium. If vapour is used,heating must be in several stages to ensure rational utilization of thevapour. This calls for several heat exchangers and considerably raisesthe cost of the apparatus.

There is an earlier known system of using condensate and takingadvantage of its heat content, by mixing the lcondensate in stages andthen pumping it in the opposite direction, from the last stage to thefirst, after which indirect heat exchange with the lye takes place.Under this system waste gas is removed from the condensate in eachmixing vessel, stage by stage. One drawback of this is that prior to theheat exchange between the condensate and the lye, the former is at apure mixing temperature and thus even the hottest partial condensate hasbeen cooled before any useful heat transfer to the lye can take place.

To overcome this drawback and ensure functional economy with thecombined condensate at a temperature equal to or higher than that of thehottest partial condensate, the present invention provides for the rstsecondary condensate undergoing expansion and then joining thecondensate from the following stage, after which the combined condensatefrom both sources is expanded again. In this way the vapour from eachexpansion vessel is constantly utilized in the following stage at lowerpressure. The condensate obtained from this process is combined withthat from the last stage and the total secondary condensate thusreceived then undergoes direct heating in successive stages, in eachcase using vapour from the previous stage at higher pressure. The finalproduct is utilized as the heating medium in a heat exchanger to warm uplye introduced under still higher pressure and flowing through thesystem from one stage to the preceding stage, in a direction opposite tothat of the steam.

Combined secondary condensate can also undergo further indirectpreheating or intermediate heating in a heat exchanger, using wastegases from a stage or stages with higher than atmospheric pressure.

The invention is explained in greater detail in the following, referencebeing made to the accompanying drawings, which show two embodiments ofthe invention in diagrammatical form.

FIG. 1 shows an arrangement without, and

FIG. 2 one with intermediate heating of condensed liquid by means ofwaste gases.

1, 2, 3, 4 and 5 in both drawings are indirectly functioning evaporatorsseen in the direction of flow of the vapour. Vapour enters evaporator 1via tube 6, yields its heat to the lye in the evaporator and condenses,whereupon the primary condensate obtained is led olf to the boiler viatube 7. The vapours resulting from the evapr: `ICC oration of the lyeare conducted through tube 8 to evaporator 2, where further lye isevaporated and the secondary vapouristaken on via tube 9 to the nextevaporator 3, the process being repeated in evaporators 4 and 5 withvapour entering them through tubes 10 and 11. Each evaporator can beisolated and by-passed. The vapour from` stage 5 goes to a water-cooledcondenser 12 via tube 13. For this purpose the vapour feed tubes 6, 8,9, 10 `and 11 arel provided with selectively operable shut-off valves60, Iand the vapour exhaust tubes 8', 9', 10', 11 and 13 are providedwith similar valves 61. The vapor conducting conduit is provided with aplurality of anged joints, one of which is Vlocated immediately inadvance of each of the tubes 8', 9',` 10', 11 and 13. When all of theevaporators are used, valves 60 and 61 are open and each of the flangedjoints in the vapor conducting conduit is provided with an imperforatediaphragm 62.- When one of the evaporators is to be isolated andby-passed, its valves 60 and 61 are closed and the diaphragm 62 in theflanged joint of the vapor conducting conduit between the vapor feed andvapor exhaust tubes of such evaporator is replacedby an annular gasketso that vapor may pass through the anged joint.

The secondary condensate from evaporator 2 is led `olf by tube 14 to anexpansion vessel 15, where it is allowed to expand. The resulting vapouris taken via tube 16 into tube, 9 to be condensed at stage 3 at lowerpressure; The condensate leaves via tube 17 and joins that fromevaporator 3 arriving via tube 181. The condensed liquid from bothsources then `enters expansion vessel 20 via tube 19 and expands. Thevapour resulting from this is conducted via tube 21 totube 10, whichleads to the next evaporator 4. The condensate from expander 20 and fromevaporator 4 is collected, via. tubes 22 and 23, in expander 24, fromwhich the resulting vapour is taken to the last evaporator 5 via tubes25 and 11. The condensate is collected via tube 26, together with thatcoming from evaporator 5 via tube 27, and pumped (by means of pump 28)into a condensate heater 30 via tube 29. Vapour for direct heating isbrought here via tube 31 leading from tube 10. The condensate warmed bythis heater 30 is taken on via pump 32 and tube 33 (in FIG. 1 only) tothe next heater 34, where it is directly heated by vapour taken fromtube 9 via tube 35. Pump 36 takes the condensate on via tube 37 to thefollowing condensate heater 38, where it is directly heated by vapourfrom tube 8 brought by tube 39. By now all the secondary condensate hasreached a temperature corresponding to that of the vapour in evaporator2 and is thus hotter than the hottest partial condensate. It is thenpumped by pump 4t) through tube 41 to a heat exchanger 42, where itwarms up the lye from stage 5 before the latter is taken back toevaporator 1 Via tube 43. After being thus cooled, the condensate isremoved from the system via tube 41a.

Lye for evaporation is introduced into the system via tube 44, whichleads to the bottom of evaporator 3, and after evaporation is taken tothe bottom of evaporator 4 via tube 45. From here it goes via tube 46 tothe bottom of evaporator 5, and then via pump 47 and tube 48 to heatexchanger 42, from which it is led to the bottom of evaporator 1 viatube 43. Tube 49 then takes the lye from evaporator 1 to the bottomrofevaporator 2. After this, it leaves the system via a tube 50 in the formof thickened lye ready for re-utilization.

Waste gases from evaporators 2, 3, 4 and 5 are removed via a single tube51, are cooled inheat exchanger 52, and then leave the system. Each ofthe evaporators 2, 3, 4 and 5 can optionally be furnished with acondensate and gas separator 53.

The system shown in FIG. 2 functions in the same way, with thedifference that the waste gases from evaporators 2 and 3 are taken viatube 54 to a separate heat exchanger 55, where they are utilized for theintermediate warming of the condensate from heater 30 arriving via pump32 and tube 56. After intermediate warming, the condensate proceeds viatube 57 to the next heater 34. After cooling, the waste gases areremoved Vfrom the system via tube ,58. A further modication could beenvisaged if the temperature of the waste gases and the condensaterender it possible and desirable: all

`the secondary condensate could be collected together in one heatexchanger for Warming up by the waste gases from all or any desirednumber of evaporators, before being taken on to the first condensateheater 30.

The invention can naturally be varied in many different ways Withoutexceeding the limits of the patent claimed. For instance, the lye warmedin heat exchanger 42 could quite easily be taken lirst to evaporator Zand from there to evaporator 1--i.e. in the opposite direction to theVapour-before it is removed from the system.

What I claim is:

l. A method of evaporating liquid, especially waste lye from the pulpindustry, in an evaporation system comprising a pluralitylof stages,each stage having a heating body and each stage operating at a differentevaporating temperature and in Which said liquid is evaporatedsimultaneously in all of said stages, which method comprises, passingthe vapor driven off during the evaporation in a particular heatingstage as a heating medium into the heating body of a stage whichoperates at a lower temperature than said particular stage and in saidlower temperature stage condensing the vapors so generated to form afirst-condensate, expanding said rst condensate in an expansion vessel,leading the vapors resulting from the expansion of said rst condensateto the heating body of a stage with still lower temperature and joiningthe expanded condensate with condensate from the said stage with stilllower temperature, expanding the condensate from both sources,constantly utilizing this expanded vapor from each expansion vessel in astage with lower temperature, combining all condensates from successiveCil stages in degrading temperature ow with respect to the ow of vaporsreleased from the successive stages and combining said condensates Withthe condensate from the stage with lowest temperature, heating the thusobtained total condensate directly in successive stages in directcontact counterow with respect to the heating vapors for the variousevaporating stages with the aidof vapor from said evaporating stages andnally using the thus heated total condensate as the heating medium in anindirect'heat exchanger to warm up liquid being introduced `into anevaporating stage which operates at a temperature no lower than the nexthigher temperature above said particular stage.

2. A method in accordance with claim 1 comprising leading the totalcondensate to a preheating stage in a heat exchanger and employing as anindirect heating medium in said heat exchanger waste gases from anevaporating stage operating at a pressure corresponding to a temperaturehigher than that of the combined condensates.

3. A method in accordance with claim l comprising leading the totalcondensate to an'intermediate heating stage between the successivedirect heating stages with regard to temperature, and in saidintermediate heating stage heating said condensate in a heat exchangeremploying as a heating medium waste gases from an evaporating stageoperating at a pressure corresponding toa temperature higher than thatof the combined condensates.

References Cited by the Examiner UNITED STATES lPATENTS y2,651,356 `9/53Sadler 159-46 X 2,734,565 2/56 Lockman 159-20 2,896,705 7/59 Ramen159-20 X 2,941,590 6/60 Rosenblad 159-20 X 2,979,442 4/61 Badger Q---159-47 NORMAN YUDKOFF, Primary Examiner.

GEORG-E D. MITCHELL, CHARLES OCONNELL,

BENJAMIN BENDETT, Examiners.

1. A METHOD OF EVAPORATING LIQUID, ESPECIALLY WASTE LYE FROM THE PULPINDUSTRY, IN AN EVAPORATIONSYSTEM COMPRISING A PLURALITY OF STAGES, ECHSTAGE HAVING AHEATING BODY AND EACH STAGE OPERATING AT A DIFFERENTEVAPORATING TEMPERATURE AND IN WHICH SAID LIQUID IS EVAPORATEDSIMULTANEOUSLY IN ALL OF SAID STAGES, WHICH METHOD COMPRISES, PASSINGTHE VAPOR DRIVEN OFF DURING THE EVAPORATION IN A PARTICULAR HEATINGSTAGE AS A HEATING MEDIUM INTO THE HEATING BODY OF A STAGE WHICHOPERATES AT A LOWER TEMPERATURE THAN SAID PARTICULAR STAGE AND IN SAIDLOWER TEMPERATURE STAGE CONDENSING THE VAPORS SO GENERATED TO FORM AFIRST CONDENSATE, EXPANDING SAID FIRST CONDENSATE IN AN EXPANSIONVESSEL, LEADING THE VAPORS RESULTING FROM THE EXPANDION OF SAID FIRSTCONDENSATE TO THE HEATING BODY OF A STAGE WITH STILLLOWER TEMPERATUREAND JOINING THE EXPANDED CONDENSATE WITH CONDENSATE FROM THE SAID STAGEWITH STILL LOER TEMPERATURE, EXPANDING THE CONDENSATE FROM BOTH SOURCES,CONSTANTLY UTILIZING THIS EXPANDED VAPOR FROM EACH EXPANSION VESSEL IN ASTAGE WITH LOWER TEMPERATURE, COMBINING ALL CONDENSATES FROM SUCCESSIVESTAGES IN DEGRADING TEMPERATURE FLOW WITH RESPECT TO THE FLOW OF VAPORSRELEASED FROM THE SUCCESSIVE STAGES AND COMBINING SAID CONDENSTES WITHTHE CONDENSATE FROM THE STAGE WITH LOWEST TEMPERATURE, HEATING THE THUSOBTAINED TOTAL CONDENSATE DIRECTLY IN SUCCESSIVE STAGES IN DIRECT CON-